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Q: I need to install some doors at my house. A friend told me to make the rough
opening for the door and frame larger than the actual door frame dimensions. He also told me that I
need to use shims to help install the door.

A: Your friend is giving you solid advice. Rough openings need to be larger for
both doors and windows so that they experience minimal or no structural stress when they are
installed. If you installed a door or window in a wall and it was tight against the rough framing
lumber on all sides, pressure could cause it to rub or stick.

The gap between the rough framing and the door or window jamb allows for the stress and loads to
be transferred around the door or window. The gaps also allow you to make fine adjustments so the
window or door operates and fits perfectly for many years.

The gaps between the outer edge of the door or window jambs and the rough framing should rarely,
if ever, be more than a half-inch.

Wood shims are used to make the door or window fit tightly in the rough opening so it doesn’t
shift around when it is operated. Shims are flat pieces of wood that can be 6 to 10 inches long and
have a taper. They can be made from any wood species, but cedar shims are easier to work with and
easier to trim with a razor knife.

When shimming a door in position, it’s usually best to start on the hinge side of the door. Most
manufacturers want to see shims at the same height as the hinges on the door; the weight of the
door is transferred to the door frame at these points.

Shims are generally installed in pairs — one shim coming from each side of the doorjamb.

You want a solid connection between the door frame and the rough opening, with no gaps. If the
rough opening is twisted because of warped lumber, you might have to install an extra single shim
to fill the gap.

Tim Carter is a columnist for Tribune Media Services. He can be reached via his website,
www.askthebuilder.com.